Hi,
1. in the commercial version, you can activate a simplified registration where you can just ask the user his email address and a user account will be generated for him automatically.
2. Indeed. Now, HikaShop has an open APi where anyone can create a shipping plugin.
3. Yes. We want to handle options (other products which can be real options like on dell's website) as well in the future.
4. Indeed. SIM has the advantage that it works everywhere, without having to setup HTTPS on your website. Now, it is possible to do a AIM plugin as well. Like for shipping plugin we also have an API for that
Thanks for your interest.